The main purpose of the proposed studies is a continued investigation in details of the development and plasticity of connections in the central visual centers. Studies will be made of how normal patterns of development are disturbed by lesions (made at different levels in the visual pathway) and alterations to sensory input (by altering eye alignment or dark-rearing). The effect of introducing these disturbances at different stages in development and in adults will be followed. The rat serves as the primary experimental animal since previous work suggests that the rat's visual system serves as an excellent model for early brain development in all mammals including primates. Some studies will involve cats. From these experiments it would be hoped to derive some general conclusions regarding the interactions of different factors controlling the development of the highly ordered, mature visual system.